Magnesium alloy

ABSTRACT

The present invention relates to creep resistant magnesium alloys. The magnesium alloy includes aluminum in an amount by mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10 percent, and the remainder being magnesium and unavoidable impurities. The nanoparticles contain Y2O3 in an amount by mass of 5 to 15 percent, ZrO2 in an amount by mass of 85 to 95 percent. The sizes of nanoparticles are in the range from 5 nm to 200 nm. The present magnesium alloys have higher creep resistance compared with conventional magnesium alloys, such as AE42 alloy.

FIELD OF THE INVENTION

The invention relates generally to magnesium alloys, more particularly,to a magnesium alloy having a high creep resistance property.

DESCRIPTION OF RELATED ART

Magnesium alloys have the lowest specific gravity among practical metalmaterials, and therefore in recent years, they have increasingly beenused in casings of portable equipment and as raw materials forautomobiles, equipments and electronic consumer products requiringlightweight components. Magnesium alloys are usually 5 to 20 percentaluminum by mass with the majority being magnesium. The use of magnesiumalloys to reduce weight in automobiles has grown approximately 20%annually since the early 1990s.

If the advantages of magnesium alloys are to be extended to currentuses, for example automobiles and electronic consumer products, severalexisting problems will have to be overcome. Four issues for the use ofmagnesium alloys are: (1) creep (i.e., continued strain under stress),(2) cost, (3) castability and (4) corrosion. Creep means a strain thatis a function of time and temperature under load. For example, thecommercial die casting magnesium alloys (AZ91D, containing aluminum,zinc and manganese; AM60 and AM50, both containing aluminum andmanganese) currently used in automobiles are limited tonear-room-temperature applications because their mechanical propertiesdecrease at higher temperatures and they are susceptible to creep athigh operating temperatures.

AE42 is a rare earth element-containing magnesium die casting alloy (Edesignates mischmetal) that has creep resistance sufficient forautomatic transmission operating temperatures (up to 150.degree. C.),but not engine temperatures (above 150.degree. C.). Another conventionalcreep resistant magnesium alloy is one that contains aluminum in anamount by mass of 1.5 to 4 percent, silicon in an amount by mass of 0.5to 1.8 percent, rhenium in an amount by mass of 0.05 to 0.6 percent,strontium in an amount by mass of 0.005 to 1.5 percent, and the balancemagnesium and unavoidable impurities.

Some magnesium alloys do provide good high-temperature properties andare used in aerospace and nuclear reactors. However, the high costs ofexotic elements (Ag, Y, Zr and rare earths) used in these alloys maketheir use in automobiles and electronic consumer products prohibitivelyexpensive. Besides, these conventional alloys contain smaller amount ofaluminum, it results in lower hardness and strength of the alloys.

What is needed, therefore, is magnesium alloys which have high creepresistance, appropriate strength and cost effectiveness.

SUMMARY OF INVENTION

In one embodiment, a magnesium alloy contains aluminum in an amount bymass of 5 to 20 percent, 0.1 to 10 percent by mass of nanoparticles inan amount by mass of 0.1 to 10 percent, with the remainder beingmagnesium and unavoidable impurities. The nanoparticles contain Y2O3 inan amount by mass of 5 to 15 percent, ZrO2 in an amount by mass of 85 to95 percent. The remainder further contains strontium in an amount bymass of 0.3 to 1.5 percent. The sizes of nanoparticles are in the rangefrom 5 nm to 200 nm.

Advantages and novel features of the present invention will become moreapparent from the following detailed description of preferredembodiments when taken in conjunction with the accompanying drawings.

BRIEF DESCRIPTION OF DRAWINGS

Many aspects of the present magnesium alloy can be better understoodwith reference to the following drawings. The components in the drawingsare not necessarily to scale, the emphasis instead being placed uponclearly illustrating the principles of the present magnesium alloy.

FIG. 1 is a schematic view of a creep resistant magnesium alloy inaccordance with a preferred embodiment; and

FIG. 2 is a graph showing a relationship between creep strain and timefor the magnesium alloy of FIG. 1.

Corresponding reference characters indicate corresponding partsthroughout the views. The exemplifications set out herein illustrate atleast one preferred embodiment of the present invention, in one form,and such exemplifications are not to be construed as limiting the scopeof the invention in any manner.

DETAILED DESCRIPTION

Reference will now be made to the drawing to describe embodiments of thepresent invention, in detail.

In one embodiment, a magnesium alloy contains aluminum in an amount bymass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10percent, with the remainder being magnesium and unavoidable impurities.The nanoparticles contain Y2O3 in an amount by mass of 5 to 15 percent,Al2O3 in an amount by mass of 3 to 8 percent, AlN in an amount by massof 1 to 3 percent, with the remainder being ZrO2. The remainder canfurther contain strontium in an amount by mass of 0.3 to 1.5 percent.The sizes of nanoparticles are in the range from 5 nm to 200 nm.Preferably, the nanoparticles are in an amount by mass of 0.5 to 2percent and the sizes of nanoparticles are in the range of 10 nm to 100nm.

In another embodiment, a magnesium alloy contains aluminum in an amountby mass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to10 percent, with the remainder being magnesium and unavoidableimpurities. The nanoparticles contains Y2O3 in an amount by mass of 5 to15 percent, Al2O3 in an amount by mass of 3 to 8 percent, and ZrO2 in anamount by mass of 77 to 92 percent. Furthermore, the remainder containsstrontium in an amount by mass of 0.3 to 1.5 percent. The sizes ofnanoparticles are in the range from 5 nm to 200 nm. Preferably, thenanoparticles are in an amount by mass of 0.5 to 2 percent and the sizesof nanoparticles are in the range from 10 nm to 100 nm.

In third embodiment, a magnesium alloy contains aluminum in an amount bymass of 5 to 20 percent, nanoparticles in an amount by mass of 0.1 to 10percent, with the remainder being magnesium and unavoidable impurities.The nanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent,and ZrO2 in an amount by mass of 85 to 95 percent. Furthermore theremainder contains strontium in an amount by mass of 0.3 to 1.5 percent.The sizes of nanoparticles are in the range from 5 nm to 200 nm.Preferably, the nanoparticles are in an amount by mass of 0.5 to 2percent and the sizes of nanoparticles are in the range from 10 nm to100 nm.

Referring to FIG. 1, the magnesium alloy 10 contains a small percentageof nanoparticles 12 that is incorporated into the magnesium-aluminumalloy 11 so as to improve the mechanical properties and reduce the creepproblems associated therewith. Also referring to FIG. 2, creep is strainunder load as a function of time. Before receiving an external load, astructure of the nanoparticles 12 is monoclinic. The structuretransforms into tetragonal phase after receiving the external load withtime. The tetragonal phases forms blocks in front of crack 13 and havehigher strength to stop crack 13 propagation in the magnesium alloy 10as shown in FIG. 1.

A key mechanical parameter of metal alloys is fracture toughness K1C.The higher value of K1c, the better mechanical performance is foralloys. K1C is proportional to σ(nc/d)0.5, where σ is yield strength; cis crack length and d is material grain size. The fracture toughness,K1C is inversely proportional to a square root of a grain size. Thesmaller the grain size, the higher the value of fracture toughness K1Cis. The nanocomposite particles of the present magnesium alloys havesmall grain sizes, so that they have high fracture toughness K1C forresisting creep.

Compared with conventional magnesium alloys, such as AE42 alloy, thepresent magnesium alloys have high creep resistance. Besides, by addingnanocomposite particles AlN, a good thermal conductor, the presentmagnesium alloys have good heat dissipation. This is an advantage whenused in electronic consumer product casting, such as notebook or laptopcomputers.

Finally, it is to be understood that the above-described embodiments areintended to illustrate rather than limit the invention. Variations maybe made to the embodiments without departing from the spirit of theinvention as claimed. The above-described embodiments illustrate thescope of the invention but do not restrict the scope of the invention.

1. A magnesium alloy comprising: aluminum in an amount by mass of 5 to20 percent; nanoparticles in an amount by mass of 0.1 to 10 percent;remainder being magnesium; and unavoidable impurities; wherein thenanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent,Al2O3 in an amount by mass of 3 to 8 percent, AlN in an amount by massof 1 to 3 percent, with the remainder being ZrO2.
 2. The magnesium alloyas claimed in claim 1, wherein the nanoparticles are in an amount bymass of 0.5 to 2 percent.
 3. The magnesium alloy as claimed in claim 1,wherein the remainder further containing strontium in an amount by massof 0.3 to 1.5 percent.
 4. The magnesium alloy as claimed in claim 1,wherein the sizes of nanoparticles are in the range from 5 nm to 200 nm.5. The magnesium alloy as claimed in claim 4, wherein the preferredsizes of nanoparticles are in the range from 10 nm to 100 nm.
 6. Amagnesium alloy comprising: aluminum in an amount by mass of 5 to 20percent; nanoparticles in an amount by mass of 0.1 to 10 percent;remainder being magnesium, and unavoidable impurities; wherein thenanoparticles contains Y2O3 in an amount by mass of 5 to 15 percent,Al2O3 in an amount by mass of 3 to 8 percent, and ZrO2 in an amount bymass of 77 to 92 percent.
 7. The magnesium alloy as claimed in claim 6,wherein the nanoparticles are in an amount by mass of 0.5 to 2 percent.8. The magnesium alloy as claimed in claim 6, wherein the remainderfurther comprises strontium in an amount by mass of 0.3 to 1.5 percent.9. The magnesium alloy as claimed in claim 6, wherein the sizes ofnanoparticles are in the range from 5 nm to 200 nm.
 10. The magnesiumalloy as claimed in claim 9, wherein the preferred sizes ofnanoparticles are in the range from 10 nm to 100 nm.
 11. A magnesiumalloy comprising: aluminum in an amount by mass of 5 to 20 percent;nanoparticles in an amount by mass of 0.1 to 10 percent; reminder beingmagnesium and unavoidable impurities; wherein the nanoparticles containsY2O3 in an amount by mass of 5 to 15 percent, and ZrO2 in an amount bymass of 85 to 95 percent.
 12. The magnesium alloy as claimed in claim11, wherein the nanoparticles are in an amount by mass of 0.5 to 2percent.
 13. The magnesium alloy as claimed in claim 11, wherein thereminder further comprises strontium in an amount by mass of 0.3 to 1.5percent.
 14. The magnesium alloy as claimed in claim 11, wherein thesizes of nanoparticles are in the range from 5 nm to 200 nm.
 15. Themagnesium alloy as claimed in claim 14, wherein the preferred sizes ofnanoparticles are in the range from 10 nm to 100 nm.